[hum4god]

Hi All
i am interested in building some open baffles .
i have been looking around for some time and saw a lot of VERY interesting and even some good looking designs.
my question is :

how do i go about to find the right size and shape for my baffle?
did you just do the trial and error method?
i kow of several plans that look nice and would fit in my space .
should i just play around and mount the driver on a cheap wood board the size of my choice?
i also heard that the height in which the driver is mounted has a big influence on the sound?
and i read something about it being best to have it off center? why?

lots of questions , but i dont think its that hard.
any and all information is welcome.
oh i almost forgot .   the driver i am looking to implemnt is Fertin 20ex .

thanks
malcolm

[Brad]

Malcolm,

Welcome to the OB forum, first of all.
I just took a look at that driver - very interesting (thanks to Google for translating from French)

If you're not sure what size you want to end up with, why not start with some basic cardboard?
Mount the driver about 2/3 of the way up.
Try it that way and then flip it 180 degrees to put the driver closer to the floor.
Your ears will tell you what is working better in your room.

To my inexperienced eye, the q of that driver is probably not going to let you make much bass in OB
That is an interesting design - I bet the mids and highs are very nice.
Are you considering supplementing the bottom end with a subwoofer?

I'll leave it to some of our more experienced members to comment further....

Cheers

[JohninCR]

Malcolm,

The truth is that there is no easy answer.

What are the specs of the Fertin?  A quick search came up blank.

How to plan to handle bass or are you going to try the Fertin alone?
If you're going to augment the bass, what kind of XO, passive or active?

Do you have or plan to use EQ?

Room size, placement flexibility, etc?  Goals for overall speaker size,
minimal preferred or larger but tasteful is OK?

Musical taste and importance of full dynamic bass to you?

Sorry, questions but no answers.  btw It's not really trial and error, more
like trial and make better, because almost anything works as long as you
get some bass.

[Rudolf]

It´s like with most things: either ...   or ...

Either you follow a proven and documented design ...
... or you become aquainted with all the physical aspects of an OB.

Sadly there is no central source dealing with baffle shapes and sizes, driver position, room influence etc. (I have tried to do that at www.dipolplus.de, but that´s in German only ).
So you will have to look around at the forums or bite some sawdust.

At least you should read (and understand) www.linkwitzlab.com/models.htm#B, better of course the complete Linkwitz site.

For a more practical approach I would recommend to download the free OB simulation program EDGE (www.tolvan.com/edge), which is really intuitive. Put a driver on a baffle and change the different parameters (but only one at a time). That´s how I learned how things are related (and controled) in OBs.

Rudolf

[Bob in St. Louis]

What are the specs of the Fertin?

Didn't find much, here's a couple numbers. You'll have to get past "Swedish/German"?? but I see a valid number or two in there.

EDIT: {nevermind.... that was the wrong driver .....  }

Bob

[nullspace]

Malcolm,

I use the Fertin 20EX on a JE Labs open baffle. Very, very nice, if a bit bass shy. I'll be working on a new baffle this summer and adding a couple 15" woofers to cover the low end. Be sure to use a 12v battery to power the field coil (something bigger than 12ah); it makes quite a difference. Also, I have a Fostex FT96H sitting on the top shelf, pointing backwards & connected out-of-phase, and crossed with a .68uf cap; works well.

Those who have heard field coil drivers find them addictive.

Specs here:
http://www.jlbcreations.com/Fertin/produits_hp.asp
JE Labs OB here:
http://members.myactv.net/~je2a3/open.htm
Thread on diyaudio concerning Fertin and OB:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=6060

Regards,
John

[JohninCR]

Nullspace,

Have you tried varying the voltage?  Your link shows that you get a Qts more
suitable going it alone with 5 to 6 volts. 

I've tried taking single drivers to the limits of OB, and there's just no way I'd
ever get the bass dynamics I want, so I've gone active with bass augmentation
and could never go back.  IMHO relieving a fullranger of handling bass duties
pays real dividends in the midrange and up whether it's OB or not.

[nullspace]

I have tried varying the voltage. However, below about 9v the sound becomes too soft, losing a lot of the effortless dynamics field coils are known for. And, efficiency goes down. No way they're near 100db efficient at 12v; maybe 94-95, tops. If you plug the t/s listed at their website into any calculator, it comes out 92 I think. I didn't measure with the lower voltage but I think we can assume that there was more bass, but at the expense of everything else. To me, 12v sounds best overall, even if the low end really only extends to 70-80hz.

A single fullrange driver can't compare to same with bass augmentation. By itself, the Fertin is not for everyone, but it does an awful lot right. Hopefully, my experiements next spring and summer will be fruitful and I'll have a bass solution to go with the tremendous 100hz and up I already experience.

Regards,
John

[hum4god]

WOW,
thank you everyone , lots of info and questions.

firstly i would like to get the fertin in the ob and see how much bass i can get , but i don't expect too much and probably have to implement some bass solution later.

for space : my room is not too big , about 12 x 15 open to one side to the kitchen.
space for the ob's is also a bit restricted . max. width would be around 24".height up to ceiling 8' , depth around 30".
dynamic bass would be nice as i am listening to all kinds of music from opera and large scale orchestra to mostly rock (radiohead , jack johnson etc) , so bass is not unimportant.

x over could be active and passive . i looked at the marchand crossovers.nice
well, if i don't have to spend too much on that , i guess for now i just want to keep it simple and get the fertin in the ob , see how it sounds and then the bass . or would it be important to include that right away?
i am not planning on eq at this point.
Bob , that is not the same driver. i will try to get the specs.
thanks
malcolm

[Bob in St. Louis]

Bob , that is not the same driver. i will try to get the specs.

  Oh, Heck....I'll remove that NOW. I'd hate for somebody to use them, only to find out there wrong. 

[nullspace]

Malcolm,

If it were me and I had your space restrictions, I'd follow Thorsten's lead:
http://www.diyaudio.com/forums/showthread.php?postid=234860#post234860
http://www.diyaudio.com/forums/showthread.php?postid=237247#post237247
24"x42" OB run fullrange (Fertins have 6mm peak to peak xmax) with a small sealed sub. I would guess that it's not as good as a full-on OB setup, but any time considerations for space and WAF rear up, compromises end up being made.

Maybe search for w-dipoles, n-dipoles, ripoles on diyaudio -- all a type of OB sub I have no experience with. Here's an example: http://www.linkwitzlab.com/woofer.htm

If bass is not unimportant to you, you'll want to think about a sub straight away, as the Fertins won't produce a whole lot of bass in this setup.

Regards,
John

[hum4god]

here is the fertin page in french with Quelques realisations.

http://www.jlbcreations.com/Fertin/exemple.asp

but i still can't find the specs.

malcolm

[nullspace]

It's here: http://www.jlbcreations.com/Fertin/produits_hp.asp
And then use the drop down to pick the 20EX.

Regards,
John

[Bob in St. Louis]

Here, I have to redeem myself for giving the wrong drivers spec earlier:

Impedance (ohms) 8
power capacity (W rms) 50
sensitivity (dB) 100
flux density (Tesla) 1.4
total flux (Mx) 200000
moving mass (g) 18
mecanical compliance (Cms m/s) 0.00085
resonance frequency (Fs Hz) 42
mechanical efficiency(Qms average) 15.813
electrical efficiency factor (Qe) 0.428
total efficiency factor (Qt) 0.416
BL factor (0) 8.26
inductance (mH) 0.25
equivalent air volume (L) 48
displacement of diaphragm (Xmax mm) +/- 3
voice coil resistance (Re ohms) 6.4
effective diaphragm area (Sd m2) 0.02
overall diameter (mm) 230/210
bolt circle diameter (mm) 216
depth (mm) 150
net weight (Kg) 8
power supply (V/A) 12,5/1,5
consumption (W) 20
GAP height (mm) 12
voice coil height (mm) 6
surround neoprene
cone paper
voice coil material copper

Thanks nullspace for finding that........  aa

[JohninCR]

I do my projects different from everyone else.  I start with the
size and look I want before anything else, and figure out how to
make it work.

Until you're ready to go active with bass augmentation my recommendation
would be to go with as large a baffle with the driver mounted as low as you
can tolerate.

Although I'm an advocate of using wings to extend bass, they are harder to
get right and you open up a can of worms with issues where there is little to
no guidance.  They include reflections off of the wings disturbing the rear
wave, cavity resonances, 1/4 wave resonances, panel vibrations, and baffle
step type behavior, because you've raised the threshold of 1/2 space launch. 
Wings do, however, force the rear wave to travel further to reach the listening
position using the same amount of wood, which increases bass extension and
you can ultimately get very good results in a size similar to box speakers.

Once you have them up and running on a temporary flat baffle, then you have
a basis for comparison and can experiment with folding using a narrow front
and easily attach temporary wings of different sizes to the back side.

I wouldn't spend too much time on getting wings right.  An 8" driver simply
can't make significant bass on OB, acceptable yes, but nowhere near keeping
up with what your Fertin can do in the rest of the range.  Plus the Fertin will
sound even better once relieved of bass duty any way.  Once you go to biamping
and active integration of your augmenter, then baffle size is out the window.
Just get a 15" driver and you don't even need a baffle.  I'm almost finished with
a nearly flat baffle for the B200 + 15" bass augmenter, which is only 17" wide
and 33" tall that should fit any room.  In addition, I'll be experimenting soon with
some ideas I have to cure edge diffraction of an 8" driver on OB without using a
big baffle to spread the effects.

Here's a sneak peak before I start cutting the hole for the augmenter.

[Bob in St. Louis]

Wow John, that's fantastic wood you've got there. You seem to be 'maturing' as a wood worker too. (That was a complement by the way.)
Not too long ago you were apologizing for your wood working skills.
I'd like to see some detail of the 'swoopys' at the top. Very nice. 

What kind of wood, and how thick is it?

Bob

[nullspace]

I have to agree with Bob; those are some damn fine looking baffles. I know it's just a picture, but they look almost as though you carved them.

Regards,
John.

[JohninCR]

Thanks guys.  It's 1" thick Cenizaro (some type of mimosa rain tree).  Believe me the pic
don't even come close.  Wait till I rub some linseed oil in and really bring out the grain. 
They're just raw wood in the pic.

All I did was cut triangles off of the last 2 rectangular pieces I had left.  I used a steep angle
for the cut, but I didn't like the look.  I took the 2 triangles and glued them to the back and hit
the leading edge of the initial cut with the belt sander to round it off, and voila.  Ssshhh.  Don't
tell anyone how easy it was, and that it was mostly luck, because that's not how I initially planned
the baffles.  The top is cut flush now and I trimmed the little wings at more of an angle, plus rounded
off all of the sharp edges.  Final pics soon.

[hum4god]

John ,
that looks absolutely stunning.respect.
i definetly think about the opyion of biaming and doing an active crossover .
but then i ahave to find out what bass driver to use that is fast enough and what enclosure etc.
what will your bass solution be ?
what driver , box , amp , crossover ?
do i understand you right that the wings would basically be an enforcement for the lower frequencies and if i dial in a sub at around 100 or 150 hz i don't have to bother about baffle size too much?
that would be great.
i still have to get in contact with someone who can show me a bit about woodworking .
the basic stuff i will learn on some cheap test baffles.
how to cut a round hole out of the baffle.
thank god i have a few friends that are woodworkers.
how did you make the rings to hold the driver?
is it the same as the baffle and just taken out ?
how would you do that ?
or a more general question : would you recommend mounting the driver on the outside and preferably in a way that it sits flush with the baffle?
how to do that technically?

thanks for all the great info

malcolm

[hum4god]

here is a review link about a german way to build a fertin ob .
scroll down and look at these beauties.

http://www.blackforestaudio.de/cms/upload/bfa/presse_testberichte/AP_03_04_HelixMammut.pdf

malcolm